Regardless of what the dealer told you, if you go with an HTT you will always need to be conscious of closing up the ends wet, and will need to open them up to dry properly later, if you do have to close them up in rain, or early morning with lots of dew on them. (just like a pop-up). It was a good eye-opener for you.
Nothing wrong with getting an HTT, you just need to be aware of water and closing up for extended periods of time afterwards.
FYI, I'd run from that camper. Even it was snow, it just doesn't sound right! There's a bazillion other choices out "there", keep looking, you won't regret it.